A turbine engine includes a compressor typically comprising a plurality of axial stages, which compress airflow in turn. A typical axial compressor includes a split outer casing having two 180 degree halves, which are suitably bolted together. The casing includes rows of axially spaced apart casing slots which extend circumferentially for mounting respective vane segments.
A typical vane segment includes a pair of 180 degree diaphragm assemblies, each diaphragm assembly comprising radially outer and inner shrouds between which are attached a plurality of circumferentially spaced apart airfoils. The outer shroud includes a pair of axially spaced apart hook elements. The casing includes complementary first and second axially spaced apart grooves, which extend circumferentially within each of the casing slots for receiving the corresponding hook elements in a tongue-and-groove mounting arrangement.
During assembly, the individual diaphragm assemblies are circumferentially inserted into respective ones of the casing halves by engaging the hook elements with the corresponding grooves. Each diaphragm assembly is slid circumferentially in turn into its casing slot. The two casing halves are then assembled together so that the diaphragm assemblies in each casing slot define a respective annular vane segment for each compression stage. In this configuration, the individual diaphragm assemblies are mounted to the outer casing solely by their outer shrouds, with the airfoils and inner shrouds being suspended therefrom.
During operation of the compressor, each vane segment experiences stage differential pressure and airflow impingement, resulting in longitudinal, circumferential, and radial loads being transferred to and through the hook elements of the diaphragm assembly. Those steady loads are combined with pulsating blade-passing aerodynamic excitation loads, which cause the airfoils and outer shrouds of the diaphragm assemblies to vibrate. The vibrations in the outer shrouds cause the hook members to move within the corresponding grooves. Such movement results in frictional wear between the outer shrouds and the engine casing, which wear reduces part life.